Size-selective opening of the blood-brain barrier by targeting endothelial sphingosine 1-phosphate receptor 1

Sphingosine 1-Phosphate in Malaria Pathogenesis and Its Implication in Therapeutic Opportunities

Sphingosine 1-Phosphate (S1P) is a bioactive lipid intermediate in the sphingolipid metabolism, which exist in two pools, intracellular and extracellular, and each pool has a different function. The circulating extracellular pool, specifically the plasma S1P is shown to be important in regulating various physiological processes related to malaria pathogenesis in recent years. Although blood cells (red blood cells and platelets), vascular endothelial cells and hepatocytes are considered as the important sources of plasma S1P, their extent of contribution is still debated. The red blood cells (RBCs) and platelets serve as a major repository of intracellular S1P due to lack, or low activity of S1P degrading enzymes, however, contribution of platelets toward maintaining plasma S1P is shown negligible under normal condition. Substantial evidences suggest platelets loss during falciparum infection as a contributing factor for severe malaria. However, platelets function as a source for plasma S1P in malaria needs to be examined experimentally. RBC being the preferential site for parasite seclusion, and having the ability of trans-cellular S1P transportation to EC upon tight cell-cell contact, might play critical role in differential S1P distribution and parasite growth. In the present review, we have summarized the significance of both the S1P pools in the context of malaria, and how the RBC content of S1P can be channelized in better ways for its possible implication in therapeutic opportunities to control malaria.

Role for caveolin-mediated transcytosis in facilitating transport of large cargoes into the brain via ultrasound

The blood-brain barrier (BBB) is a dynamic diffusional barrier regulating the molecular and chemical flux between the blood and brain, thereby preserving cerebral homeostasis. Endothelial cells form the core anatomical component of the BBB based on properties such as specialized junctional complexes between cells, which restricts paracellular transport, and extremely low levels of vesicular transport, restricting transcytosis. In performing its protective function, the BBB also constrains the entry of therapeutics into the brain, hampering the treatment of various neurological disorders. Focused ultrasound is a novel therapeutic modality that has shown efficacy in transiently and non-invasively opening the BBB for the targeted delivery of therapeutics to the brain. Although the ability of ultrasound to disrupt the junctional assembly of endothelial cells has been partially investigated, its effect on the transcellular mode of transport has been largely neglected. In this study, we found that ultrasound induces a pronounced increase in the levels of the vesicle-forming protein caveolin-1. In order to investigate the role of vesicle-mediated transcytoplasmic transport, we compared the leakage of various cargo sizes between a mouse model that lacks caveolin-1 and wild-type mice following sonication of the hippocampus. The absence of caveolin-1 did not lead to overt abnormalities in the cerebral vasculature in the mice. We found that caveolin-1 has a critical role specifically in the transport of large (500 kDa), but not smaller (3 and 70 kDa) cargoes. Our findings indicate differential effects of therapeutic ultrasound on cellular transport mechanisms, with implications for therapeutic interventions.

Serum Sphingosine 1-Phosphate (S1P): A Novel Diagnostic Biomarker in Early Acute Ischemic Stroke

Background: Sphingosine 1-phosphate (S1P) is a lipid metabolite that mediates various physiological processes, including vascular endothelial cell function, inflammation, coagulation/thrombosis, and angiogenesis. As a result, S1P may contribute to the pathogenesis of stroke.

Objective: This study aimed to evaluate the diagnostic value of serum S1P in acute stroke.

Method: A total of 72 patients with ischemic stroke, 36 patients with hemorrhagic stroke, and 65 controls were enrolled. Serum S1P was detected by enzyme-linked immunosorbent assay (ELISA).

Results: Receiver operating characteristic curve analysis demonstrated that serum S1P could discriminate ischemic stroke from hemorrhagic stroke in both total population and subgroup analyses of samples obtained within 24 h of symptom onset (subgroup _{< 24h}) (area under curve, AUC_Total = 0.64, P = 0.017; AUC_{Subgroup < 24h} = 0.91, P < 0.001) and controls (AUC_Total = 0.62, P = 0.013; AUC_{Subgroup <24h} = 0.83, P < 0.001). Furthermore, S1P showed higher efficacy than high-density lipoprotein cholesterol (HDL-C) in discriminating ischemic stroke from controls in the total population (P_S1P = 0.013, P_HDL−C = 0.366) and in the subgroup analysis (i.e., <24 h; P_S1P < 0.001, P_HDL−C = 0.081). Additionally, lower serum S1P was associated with cervical artery plaques (P = 0.021) in controls and with dyslipidemia (P = 0.036) and milder neurological impairment evaluated by the National Institute of Health Stroke Scale (NIHSS, P = 0.047) in the ischemic stroke group.

Conclusions: The present study preliminarily investigated the diagnostic value of serum S1P in acute stroke. Decreased serum S1P may become a potential biomarker for early acute ischemic stroke and can indicate disease severity.

A Sphingosine-1-Phosphate Receptor Modulator Attenuated Secondary Brain Injury and Improved Neurological Functions of Mice after ICH

Background

Stroke activates the immune system and induces brain infiltration by immune cells, aggravating brain injury. Poststroke immunomodulation via (S1P-)receptor modulation is beneficial; however, the S1P-modulator in clinical use (FTY-720) is unspecific, and undesirable side effects have been reported. Previously, we tested effects of a novel selective S1P-receptor modulator, Siponimod, on ICH-induced brain injury in acute stage of the disease. In the current study, we investigated whether protective effects of Siponimod, evaluated in a short-term study, will protect the brain of ICH animals at long term as well.

Methods

134 C57BL/6N mice were divided into sham and ICH-operated groups. Collagenase model of ICH was employed. ICH animals were divided into Siponimod treated and nontreated. Dose- and time-dependent effects of Siponimod were investigated. Contraplay between development of brain injury and the number of lymphocytes infiltrating the brain was investigated by forelimb placing, T-Maze test, brain water content calculation, MRI scanning, and immunostaining.

Results

Depending on the therapeutic strategy, Siponimod attenuated the development of brain edema, decreased ICH-induced ventriculomegaly and improved neurological functions of animals after ICH. It was associated with less lymphocytes in the brain of ICH animals.

Conclusion

Siponimod is able to decrease the brain injury and improves neurological functions of animals after ICH.

Development of an endothelial cell-restricted transgenic reporter rat: a resource for physiological studies of vascular biology

Here, we report the generation of a Cre-recombinase (iCre) transgenic rat, where iCre is driven using a vascular endothelial-cadherin (CDH5) promoter. The CDH5 promoter was cloned from rat pulmonary microvascular endothelial cells and demonstrated ~60% similarity to the murine counterpart. The cloned rat promoter was 2,508 bp, it extended 79 bp beyond the transcription start site, and it was 22,923 bp upstream of the translation start site. The novel promoter was cloned upstream of codon-optimized iCre and subcloned into a Sleeping Beauty transposon vector for transpositional transgenesis in Sprague-Dawley rats. Transgenic founders were generated and selected for iCre expression. Crossing the CDH5-iCre rat with a tdTomato reporter rat resulted in progeny displaying endothelium-restricted fluorescence. tdTomato fluorescence was prominent in major arteries and veins, and it was similar in males and females. Quantitative analysis of the carotid artery and the jugular vein revealed that, on average, more than 50% of the vascular surface area exhibited strong fluorescence. tdTomato fluorescence was observed in the circulations of every tissue tested. The microcirculation in all tissues tested displayed homogenous fluorescence. Fluorescence was examined across young (6-7.5 mo), middle (14-16.5 mo), and old age (17-19.5 mo) groups. Although tdTomato fluorescence was seen in middle- and old-age animals, the intensity of the fluorescence was significantly reduced compared with that seen in the young rats. Thus, this endothelium-restricted transgenic rat offers a novel platform to test endothelial microheterogeneity within all vascular segments, and it provides exceptional resolution of endothelium within-organ microcirculation for application to translational disease models.NEW & NOTEWORTHY The use of transgenic mice has been instrumental in advancing molecular insight of physiological processes, yet these models oftentimes do not faithfully recapitulate human physiology and pathophysiology. Rat models better replicate some human conditions, like Group 1 pulmonary arterial hypertension. Here, we report the development of an endothelial cell-restricted transgenic reporter rat that has broad application to vascular biology. This first-in-kind model offers exceptional endothelium-restricted tdTomato expression, in both conduit vessels and the microcirculations of organs.

Targeting nanoparticles to the brain by exploiting the blood-brain barrier impermeability to selectively label the brain endothelium

Current strategies to direct therapy-loaded nanoparticles to the brain rely on functionalizing nanoparticles with ligands which bind target proteins associated with the blood-brain barrier (BBB). However, such strategies have significant brain-specificity limitations, as target proteins are not exclusively expressed at the brain microvasculature. Therefore, novel strategies which exploit alternative characteristics of the BBB are required to overcome nonspecific nanoparticle targeting to the periphery, thereby increasing drug efficacy and reducing detrimental peripheral side effects. Here, we present a simple, yet counterintuitive, brain-targeting strategy which exploits the higher impermeability of the BBB to selectively label the brain endothelium. This is achieved by harnessing the lower endocytic rate of brain endothelial cells (a key feature of the high BBB impermeability) to promote selective retention of free, unconjugated protein-binding ligands on the surface of brain endothelial cells compared to peripheral endothelial cells. Nanoparticles capable of efficiently binding to the displayed ligands (i.e., labeled endothelium) are consequently targeted specifically to the brain microvasculature with minimal "off-target" accumulation in peripheral organs. This approach therefore revolutionizes brain-targeting strategies by implementing a two-step targeting method which exploits the physiology of the BBB to generate the required brain specificity for nanoparticle delivery, paving the way to overcome targeting limitations and achieve clinical translation of neurological therapies. In addition, this work demonstrates that protein targets for brain delivery may be identified based not on differential tissue expression, but on differential endocytic rates between the brain and periphery.

S1PR1 regulates the quiescence of lymphatic vessels by inhibiting laminar shear stress-dependent VEGF-C signaling

During the growth of lymphatic vessels (lymphangiogenesis), lymphatic endothelial cells (LECs) at the growing front sprout by forming filopodia. Those tip cells are not exposed to circulating lymph, as they are not lumenized. In contrast, LECs that trail the growing front are exposed to shear stress, become quiescent, and remodel into stable vessels. The mechanisms that coordinate the opposed activities of lymphatic sprouting and maturation remain poorly understood. Here, we show that the canonical tip cell marker Delta-like 4 (DLL4) promotes sprouting lymphangiogenesis by enhancing VEGF-C/VEGF receptor 3 (VEGFR3) signaling. However, in lumenized lymphatic vessels, laminar shear stress (LSS) inhibits the expression of DLL4, as well as additional tip cell markers. Paradoxically, LSS also upregulates VEGF-C/VEGFR3 signaling in LECs, but sphingosine 1-phosphate receptor 1 (S1PR1) activity antagonizes LSS-mediated VEGF-C signaling to promote lymphatic vascular quiescence. Correspondingly, S1pr1 loss in LECs induced lymphatic vascular hypersprouting and hyperbranching, which could be rescued by reducing Vegfr3 gene dosage in vivo. In addition, S1PR1 regulates lymphatic vessel maturation by inhibiting RhoA activity to promote membrane localization of the tight junction molecule claudin-5. Our findings suggest a potentially new paradigm in which LSS induces quiescence and promotes the survival of LECs by downregulating DLL4 and enhancing VEGF-C signaling, respectively. S1PR1 dampens LSS/VEGF-C signaling, thereby preventing sprouting from quiescent lymphatic vessels. These results also highlight the distinct roles that S1PR1 and DLL4 play in LECs when compared with their known roles in the blood vasculature.

Physiological blood-brain transport is impaired with age by a shift in transcytosis

The vascular interface of the brain, known as the blood-brain barrier (BBB), is understood to maintain brain function in part via its low transcellular permeability^1-3. Yet, recent studies have demonstrated that brain ageing is sensitive to circulatory proteins^4,5. Thus, it is unclear whether permeability to individually injected exogenous tracers-as is standard in BBB studies-fully represents blood-to-brain transport. Here we label hundreds of proteins constituting the mouse blood plasma proteome, and upon their systemic administration, study the BBB with its physiological ligand. We find that plasma proteins readily permeate the healthy brain parenchyma, with transport maintained by BBB-specific transcriptional programmes. Unlike IgG antibody, plasma protein uptake diminishes in the aged brain, driven by an age-related shift in transport from ligand-specific receptor-mediated to non-specific caveolar transcytosis. This age-related shift occurs alongside a specific loss of pericyte coverage. Pharmacological inhibition of the age-upregulated phosphatase ALPL, a predicted negative regulator of transport, enhances brain uptake of therapeutically relevant transferrin, transferrin receptor antibody and plasma. These findings reveal the extent of physiological protein transcytosis to the healthy brain, a mechanism of widespread BBB dysfunction with age and a strategy for enhanced drug delivery.

G Protein-Coupled Receptors in the Mammalian Blood-Brain Barrier

The mammalian neurovascular unit (NVU) is comprised of neurons, glia, and vascular cells. The NVU is the nexus between the cardiovascular and central nervous system (CNS). The central component of the NVU is the blood-brain barrier (BBB) which consists of a monolayer of tightly connected endothelial cells covered by pericytes and further surrounded by astrocytic endfeet. In addition to preventing the diffusion of toxic species into the CNS, the BBB endothelium serves as a dynamic regulatory system facilitating the transport of molecules from the bloodstream to the brain and vis versa. The structural integrity and transport functions of the BBB are maintained, in part, by an orchestra of membrane receptors and transporters including members of the superfamily of G protein-coupled receptors (GPCRs). Here, we provide an overview of GPCRs known to regulate mammalian BBB structure and function and discuss how dysregulation of these pathways plays a role in various neurodegenerative diseases.

Improvement of Impaired Motor Functions by Human Dental Exfoliated Deciduous Teeth Stem Cell-Derived Factors in a Rat Model of Parkinson's Disease

Parkinson's disease (PD) is a long-term degenerative disease of the central nervous system (CNS) that primarily affects the motor system. So far there is no effective treatment for PD, only some drugs, surgery, and comprehensive treatment can alleviate the symptoms of PD. Stem cells derived from human exfoliated deciduous teeth (SHED), mesenchymal stem cells derived from dental pulp, may have promising potential in regenerative medicine. In this study, we examine the therapeutic effect of SHED-derived conditioned medium (SHED-CM) in a rotenone-induced PD rat model. Intravenous administration of SHED-CM generated by standardized procedures significantly improved the PD symptoms accompanied with increased tyrosine hydroxylase amounts in the striatum, and decreased α-synuclein levels in both the nigra and striatum, from rotenone-treated rats. In addition, this SHED-CM treatment decreased both Iba-1 and CD4 levels in these brain areas. Gene ontology analysis indicated that the biological process of genes affected by SHED-CM was primarily implicated in neurodevelopment and nerve regeneration. The major constituents of SHED-CM included insulin-like growth factor binding protein-6 (IGFBP-6), tissue inhibitor of metalloproteinase (TIMP)-2, TIMP-1, and transforming growth factor 1 (TGF-1). RNA-sequencing (RNA-seq) and Ingenuity Pathway Analysis (IPA) revealed that these factors may ameliorate PD symptoms through modulating the cholinergic synapses, calcium signaling pathways, serotoninergic synapses, and axon guidance. In conclusion, our data indicate that SHED-CM contains active constituents that may have promising efficacy to alleviate PD.

Mfsd2a and Spns2 are essential for sphingosine-1-phosphate transport in the formation and maintenance of the blood-brain barrier

To maintain brain homeostasis, a unique interface known as the blood-brain barrier (BBB) is formed between the blood circulation and the central nervous system (CNS). Major facilitator superfamily domain-containing 2a (Mfsd2a) is a specific marker of the BBB. However, the mechanism by which Mfsd2a influences the BBB is poorly understood. In this study, we demonstrated that Mfsd2a is essential for sphingosine-1-phosphate (S1P) export from endothelial cells in the brain. We found that Mfsd2a and Spinster homolog 2 (Spns2) form a protein complex to ensure the efficient transport of S1P. Furthermore, the S1P-rich microenvironment in the extracellular matrix (ECM) in the vascular endothelium dominates the formation and maintenance of the BBB. We demonstrated that different concentrations of S1P have different effects on BBB integrity. These findings help to unravel the mechanism by which S1P regulates BBB and also provide previously unidentified insights into the delivery of neurological drugs in the CNS.

Tight junction modulation at the blood-brain barrier: Current and future perspectives

The blood-brain barrier (BBB) is the one of the most robust physical barriers in the body, comprised of tight junction (TJ) proteins in brain microvascular endothelial cells. The need for drugs to treat central nervous systems diseases is ever increasing, however the presence of the BBB significantly hampers the uptake of drugs into the brain. To overcome or circumvent the barrier, many kinds of techniques are being developed. Modulating the paracellular route by disruption of the TJ complex has been proposed as a potential drug delivery system to treat brain diseases, however, it has several limitations and is still in a developmental stage. However, recent significant advance in medical equipment /tools such as targeted ultra-sound technologies may resolve these limitations. In this review, we introduce recent advances in site- or molecular size-selective BBB disruption/modulation technologies and we include details on pharmacological inhibitory molecules against intercellular TJ proteins to modulate the BBB.

Brain Microvascular Pericytes in Vascular Cognitive Impairment and Dementia

Pericytes are unique, multi-functional mural cells localized at the abluminal side of the perivascular space in microvessels. Originally discovered in 19th century, pericytes had drawn less attention until decades ago mainly due to lack of specific markers. Recently, however, a growing body of evidence has revealed that pericytes play various important roles: development and maintenance of blood–brain barrier (BBB), regulation of the neurovascular system (e.g., vascular stability, vessel formation, cerebral blood flow, etc.), trafficking of inflammatory cells, clearance of toxic waste products from the brain, and acquisition of stem cell-like properties. In the neurovascular unit, pericytes perform these functions through coordinated crosstalk with neighboring cells including endothelial, glial, and neuronal cells. Dysfunction of pericytes contribute to a wide variety of diseases that lead to cognitive impairments such as cerebral small vessel disease (SVD), acute stroke, Alzheimer’s disease (AD), and other neurological disorders. For instance, in SVDs, pericyte degeneration leads to microvessel instability and demyelination while in stroke, pericyte constriction after ischemia causes a no-reflow phenomenon in brain capillaries. In AD, which shares some common risk factors with vascular dementia, reduction in pericyte coverage and subsequent microvascular impairments are observed in association with white matter attenuation and contribute to impaired cognition. Pericyte loss causes BBB-breakdown, which stagnates amyloid β clearance and the leakage of neurotoxic molecules into the brain parenchyma. In this review, we first summarize the characteristics of brain microvessel pericytes, and their roles in the central nervous system. Then, we focus on how dysfunctional pericytes contribute to the pathogenesis of vascular cognitive impairment including cerebral ‘small vessel’ and ‘large vessel’ diseases, as well as AD. Finally, we discuss therapeutic implications for these disorders by targeting pericytes.

Sphingosine 1-phosphate and inflammation

AbstractSphingosine 1-phosphate (S1P), a sphingolipid mediator, regulates various cellular functions via high-affinity G protein-coupled receptors, S1P1-5. The S1P-S1P receptor signaling system plays important roles in lymphocyte trafficking and maintenance of vascular integrity, thus contributing to the regulation of complex inflammatory processes. S1P is enriched in blood and lymph while maintained low in intracellular or interstitial fluids, creating a steep S1P gradient that is utilized to facilitate efficient egress of lymphocytes from lymphoid organs. Blockage of the S1P-S1P receptor signaling system results in a marked decrease in circulating lymphocytes because of a failure of lymphocyte egress from lymphoid organs. This provides a basis of immunomodulatory drugs targeting S1P1 receptor such as FTY720, an immunosuppressive drug approved in 2010 as the first oral treatment for relapsing-remitting multiple sclerosis. The S1P-S1P receptor signaling system also plays important roles in maintenance of vascular integrity since it suppresses sprouting angiogenesis and regulates vascular permeability. Dysfunction of the S1P-S1P receptor signaling system results in various vascular defects, such as exaggerated angiogenesis in developing retina and augmented inflammation due to increased permeability. Endothelial-specific deletion of S1P1 receptor in mice fed high-fat diet leads to increased formation of atherosclerotic lesions. This review highlights the importance of the S1P-S1P receptor signaling system in inflammatory processes. We also describe our recent findings regarding a specific S1P chaperone, apolipoprotein M, that anchors to high-density lipoprotein and contributes to shaping the endothelial-protective and anti-inflammatory properties of high-density lipoprotein.

CD4 T cell sphingosine 1-phosphate receptor (S1PR)1 and S1PR4 and endothelial S1PR2 regulate afferent lymphatic migration

Sphingosine 1-phosphate (S1P) and S1P receptors (S1PRs) regulate migration of lymphocytes out of thymus to blood and lymph nodes (LNs) to efferent lymph, whereas their role in other tissue sites is not known. Here, we investigated the question of how these molecules regulate leukocyte migration from tissues through afferent lymphatics to draining LNs (dLNs). S1P, but not other chemokines, selectively enhanced human and murine CD4 T cell migration across lymphatic endothelial cells (LECs). T cell S1PR1 and S1PR4, and LEC S1PR2, were required for migration across LECs and into lymphatic vessels and dLNs. S1PR1 and S1PR4 differentially regulated T cell motility and vascular cell adhesion molecule-1 (VCAM-1) binding. S1PR2 regulated LEC layer structure, permeability, and expression of the junction molecules VE-cadherin, occludin, and zonulin-1 through the ERK pathway. S1PR2 facilitated T cell transcellular migration through VCAM-1 expression and recruitment of T cells to LEC migration sites. These results demonstrated distinct roles for S1PRs in comodulating T cell and LEC functions in migration and suggest previously unknown levels of regulation of leukocytes and endothelial cells during homeostasis and immunity.

Sphingosine 1-phosphate: Lipid signaling in pathology and therapy

Sphingosine 1-phosphate (S1P), a metabolic product of cell membrane sphingolipids, is bound to extracellular chaperones, is enriched in circulatory fluids, and binds to G protein-coupled S1P receptors (S1PRs) to regulate embryonic development, postnatal organ function, and disease. S1PRs regulate essential processes such as adaptive immune cell trafficking, vascular development, and homeostasis. Moreover, S1PR signaling is a driver of multiple diseases. The past decade has witnessed an exponential growth in this field, in part because of multidisciplinary research focused on this lipid mediator and the application of S1PR-targeted drugs in clinical medicine. This has revealed fundamental principles of lysophospholipid mediator signaling that not only clarify the complex and wide ranging actions of S1P but also guide the development of therapeutics and translational directions in immunological, cardiovascular, neurological, inflammatory, and fibrotic diseases.

Antibody transcytosis across brain endothelial-like cells occurs nonspecifically and independent of FcRn

The blood-brain barrier (BBB) hinders the brain delivery of therapeutic immunoglobulin γ (IgG) antibodies. Evidence suggests that IgG-specific processing occurs within the endothelium of the BBB, but any influence on transcytosis remains unclear. Here, involvement of the neonatal Fc receptor (FcRn), which mediates IgG recycling and transcytosis in peripheral endothelium, was investigated by evaluating the transcytosis of IgGs with native or reduced FcRn engagement across human induced pluripotent stem cell-derived brain endothelial-like cells. Despite differential trafficking, the permeability of all tested IgGs were comparable and remained constant irrespective of concentration or competition with excess IgG, suggesting IgG transcytosis occurs nonspecifically and originates from fluid-phase endocytosis. Comparison with the receptor-enhanced permeability of transferrin indicates that the phenomena observed for IgG is ubiquitous for most macromolecules. However, increased permeability was observed for macromolecules with biophysical properties known to engage alternative endocytosis mechanisms, highlighting the importance of biophysical characterizations in assessing transcytosis mechanisms.

FTY720 Protects Against Ischemia-Reperfusion Injury by Preventing the Redistribution of Tight Junction Proteins and Decreases Inflammation in the Subacute Phase in an Experimental Stroke Model

Injury due to brain ischemia followed by reperfusion (I/R) may be an important therapeutic target in the era of thrombectomy. FTY720, a widely known sphingosine-1-phosphate receptor agonist, exerts various neuroprotective effects. The aim of this study was to examine the protective effect of FTY720 with respect to I/R injury, especially focusing on blood-brain barrier (BBB) protection and anti-inflammatory effects. Male rats were subjected to transient ischemia and administered vehicle or 0.5 or 1.5 mg/kg of FTY720 immediately before reperfusion. Positron emission tomography (PET) with [¹⁸F]DPA-714 was performed 2 and 9 days after the insult to serially monitor neuroinflammation. Bovine and rat brain microvascular endothelial cells (MVECs) were also subjected to oxygen-glucose deprivation (OGD) and reperfusion, and administered FTY720, phosphorylated-FTY720 (FTY720-P), or their inhibitor. FTY720 dose-dependently reduced cell death, the infarct size, cell death including apoptosis, and inflammation. It also ameliorated BBB disruption and neurological deficits compared to in the vehicle group. PET indicated that FTY720 significantly inhibited the worsening of inflammation in later stages. FTY720-P significantly prevented the intracellular redistribution of tight junction proteins but did not increase their mRNA expression. These results suggest that FTY720 can ameliorate I/R injury by protecting the BBB and regulating neuroinflammation.

Sphingosine 1-phosphate-regulated transcriptomes in heterogenous arterial and lymphatic endothelium of the aorta

Despite the medical importance of G protein-coupled receptors (GPCRs), in vivo cellular heterogeneity of GPCR signaling and downstream transcriptional responses are not understood. We report the comprehensive characterization of transcriptomes (bulk and single-cell) and chromatin domains regulated by sphingosine 1-phosphate receptor-1 (S1PR1) in adult mouse aortic endothelial cells. First, S1PR1 regulates NFκB and nuclear glucocorticoid receptor pathways to suppress inflammation-related mRNAs. Second, S1PR1 signaling in the heterogenous endothelial cell (EC) subtypes occurs at spatially-distinct areas of the aorta. For example, a transcriptomically distinct arterial EC population at vascular branch points (aEC1) exhibits ligand-independent S1PR1/ß-arrestin coupling. In contrast, circulatory S1P-dependent S1PR1/ß-arrestin coupling was observed in non-branch point aEC2 cells that exhibit an inflammatory gene expression signature. Moreover, S1P/S1PR1 signaling regulates the expression of lymphangiogenic and inflammation-related transcripts in an adventitial lymphatic EC (LEC) population in a ligand-dependent manner. These insights add resolution to existing concepts of endothelial heterogeneity, GPCR signaling and S1P biology.

Downregulation of S1P Lyase Improves Barrier Function in Human Cerebral Microvascular Endothelial Cells Following an Inflammatory Challenge

Sphingosine 1-phosphate (S1P) is a key bioactive lipid that regulates a myriad of physiological and pathophysiological processes, including endothelial barrier function, vascular tone, vascular inflammation, and angiogenesis. Various S1P receptor subtypes have been suggested to be involved in the regulation of these processes, whereas the contribution of intracellular S1P (iS1P) through intracellular targets is little explored. In this study, we used the human cerebral microvascular endothelial cell line HCMEC/D3 to stably downregulate the S1P lyase (SPL-kd) and evaluate the consequences on endothelial barrier function and on the molecular factors that regulate barrier tightness under normal and inflammatory conditions. The results show that in SPL-kd cells, transendothelial electrical resistance, as a measure of barrier integrity, was regulated in a dual manner. SPL-kd cells had a delayed barrier build up, a shorter interval of a stable barrier, and, thereafter, a continuous breakdown. Contrariwise, a protection was seen from the rapid proinflammatory cytokine-mediated barrier breakdown. On the molecular level, SPL-kd caused an increased basal protein expression of the adherens junction molecules PECAM-1, VE-cadherin, and β-catenin, increased activity of the signaling kinases protein kinase C, AMP-dependent kinase, and p38-MAPK, but reduced protein expression of the transcription factor c-Jun. However, the only factors that were significantly reduced in TNFα/SPL-kd compared to TNFα/control cells, which could explain the observed protection, were VCAM-1, IL-6, MCP-1, and c-Jun. Furthermore, lipid profiling revealed that dihydro-S1P and S1P were strongly enhanced in TNFα-treated SPL-kd cells. In summary, our data suggest that SPL inhibition is a valid approach to dampenan inflammatory response and augmente barrier integrity during an inflammatory challenge.

FGF21 Protects against Aggravated Blood-Brain Barrier Disruption after Ischemic Focal Stroke in Diabetic db/db Male Mice via Cerebrovascular PPARγ Activation

Recombinant fibroblast growth factor 21 (rFGF21) has been shown to be potently beneficial for improving long-term neurological outcomes in type 2 diabetes mellitus (T2DM) stroke mice. Here, we tested the hypothesis that rFGF21 protects against poststroke blood–brain barrier (BBB) damage in T2DM mice via peroxisome proliferator-activated receptor gamma (PPARγ) activation in cerebral microvascular endothelium. We used the distal middle cerebral occlusion (dMCAO) model in T2DM mice as well as cultured human brain microvascular endothelial cells (HBMECs) subjected to hyperglycemic and inflammatory injury in the current study. We detected a significant reduction in PPARγ DNA-binding activity in the brain tissue and mRNA levels of BBB junctional proteins and PPARγ-targeting gene CD36 and FABP4 in cerebral microvasculature at 24 h after stroke. Ischemic stroke induced a massive BBB leakage two days after stroke in T2DM mice compared to in their lean controls. Importantly, all abnormal changes were significantly prevented by rFGF21 administration initiated at 6 h after stroke. Our in vitro experimental results also demonstrated that rFGF21 protects against hyperglycemia plus interleukin (IL)-1β-induced transendothelial permeability through upregulation of junction protein expression in an FGFR1 activation and PPARγ activity elevation-dependent manner. Our data suggested that rFGF21 has strong protective effects on acute BBB leakage after diabetic stroke, which is partially mediated by increasing PPARγ DNA-binding activity and mRNA expression of BBB junctional complex proteins. Together with our previous investigations, rFGF21 might be a promising candidate for treating diabetic stroke.

Endothelial sphingosine 1-phosphate receptors promote vascular normalization and antitumor therapy

Tumor progression is dependent on angiogenesis, which supplies nutrients and enables gas exchange and metastatic dissemination. However, tumor vessels are dysfunctional and immature, which hinders the effectiveness of various therapeutics. Sphingosine 1-phosphate receptors in endothelial cells are essential for developmental angiogenesis and physiological functions such as the maintenance of the vascular barrier and vascular tone. This study shows that endothelial sphingosine 1-phosphate receptors determine the tumor vascular phenotype and maturation and that function of S1P receptor-1 is needed for tumor vascular normalization, which allows better blood circulation and enhances antitumor therapeutic efficacy in mouse models.

Sphingosine 1-phosphate receptor-1 (S1PR1) is essential for embryonic vascular development and maturation. In the adult, it is a key regulator of vascular barrier function and inflammatory processes. Its roles in tumor angiogenesis, tumor growth, and metastasis are not well understood. In this paper, we show that S1PR1 is expressed and active in tumor vessels. Murine tumor vessels that lack S1PR1 in the vascular endothelium (S1pr1 ECKO) show excessive vascular sprouting and branching, decreased barrier function, and poor perfusion accompanied by loose attachment of pericytes. Compound knockout of S1pr1, 2, and 3 genes further exacerbated these phenotypes, suggesting compensatory function of endothelial S1PR2 and 3 in the absence of S1PR1. On the other hand, tumor vessels with high expression of S1PR1 (S1pr1 ECTG) show less branching, tortuosity, and enhanced pericyte coverage. Larger tumors and enhanced lung metastasis were seen in S1pr1 ECKO, whereas S1pr1 ECTG showed smaller tumors and reduced metastasis. Furthermore, antitumor activity of a chemotherapeutic agent (doxorubicin) and immune checkpoint inhibitor blocker (anti-PD-1 antibody) were more effective in S1pr1 ECTG than in the wild-type counterparts. These data suggest that tumor endothelial S1PR1 induces vascular normalization and influences tumor growth and metastasis, thus enhancing antitumor therapies in mouse models. Strategies to enhance S1PR1 signaling in tumor vessels may be an important adjunct to standard cancer therapy of solid tumors.

Overview of Crosstalk Between Multiple Factor of Transcytosis in Blood Brain Barrier

Blood brain barrier (BBB) conserves unique regulatory system to maintain barrier tightness while allowing adequate transport between neurovascular units. This mechanism possess a challenge for drug delivery, while abnormality may result in pathogenesis. Communication between vascular and neural system is mediated through paracellular and transcellular (transcytosis) pathway. Transcytosis itself showed dependency with various components, focusing on caveolae-mediated. Among several factors, intense communication between endothelial cells, pericytes, and astrocytes is the key for a normal development. Regulatory signaling pathway such as VEGF, Notch, S1P, PDGFβ, Ang/Tie, and TGF-β showed interaction with the transcytosis steps. Recent discoveries showed exploration of various factors which has been proven to interact with one of the process of transcytosis, either endocytosis, endosomal rearrangement, or exocytosis. As well as providing a hypothetical regulatory pathway between each factors, specifically miRNA, mechanical stress, various cytokines, physicochemical, basement membrane and junctions remodeling, and crosstalk between developmental regulatory pathways. Finally, various hypotheses and probable crosstalk between each factors will be expressed, to point out relevant research application (Drug therapy design and BBB-on-a-chip) and unexplored terrain.

Differential Expression of SMAD Genes and S1PR1 on Circulating CD4+ T Cells in Multiple Sclerosis and Crohn's Disease

The Th17 immune response plays a key role in autoimmune diseases such as multiple sclerosis (MS) and inflammatory bowel disease (IBD). Expression of Th17-related genes in inflamed tissues has been reported in autoimmune diseases. However, values are frequently obtained using invasive methods. We aimed to identify biomarkers of MS in an accessible sample, such as blood, by quantifying the relative expression of 91 Th17-related genes in CD4+ T lymphocytes from patients with MS during a relapse or during a remitting phase. We also compared our findings with those of healthy controls. After confirmation in a validation cohort, expression of SMAD7 and S1PR1 mRNAs was decreased in remitting disease (-2.3-fold and -1.3-fold, respectively) and relapsing disease (-2.2-fold and -1.3-fold, respectively). No differential expression was observed for other SMAD7-related genes, namely, SMAD2, SMAD3, and SMAD4. Under-regulation of SMAD7 and S1PR1 was also observed in another autoimmune disease, Crohn's disease (CD) (-4.6-fold, -1.6-fold, respectively), suggesting the presence of common markers for autoimmune diseases. In addition, expression of TNF, SMAD2, SMAD3, and SMAD4 were also decreased in CD (-2.2-fold, -1.4-fold, -1.6-fold, and -1.6-fold, respectively). Our study suggests that expression of SMAD7 and S1PR1 mRNA in blood samples are markers for MS and CD, and TNF, SMAD2, SMAD3, and SMAD4 for CD. These genes could prove useful as markers of autoimmune diseases, thus obviating the need for invasive methods.

Druggable Sphingolipid Pathways: Experimental Models and Clinical Opportunities

Intensive research in the field of sphingolipids has revealed diverse roles in cell biological responses and human health and disease. This immense molecular family is primarily represented by the bioactive molecules ceramide, sphingosine, and sphingosine 1-phosphate (S1P). The flux of sphingolipid metabolism at both the subcellular and extracellular levels provides multiple opportunities for pharmacological intervention. The caveat is that perturbation of any single node of this highly regulated flux may have effects that propagate throughout the metabolic network in a dramatic and sometimes unexpected manner. Beginning with S1P, the receptors for which have thus far been the most clinically tractable pharmacological targets, this review will describe recent advances in therapeutic modulators targeting sphingolipids, their chaperones, transporters, and metabolic enzymes.

The blood-brain barrier and blood-tumour barrier in brain tumours and metastases

For a blood-borne cancer therapeutic agent to be effective, it must cross the blood vessel wall to reach cancer cells in adequate quantities, and it must overcome the resistance conferred by the local microenvironment around cancer cells. The brain microenvironment can thwart the effectiveness of drugs against primary brain tumours as well as brain metastases. In this Review, we highlight the cellular and molecular components of the blood-brain barrier (BBB), a specialized neurovascular unit evolved to maintain brain homeostasis. Tumours are known to compromise the integrity of the BBB, resulting in a vasculature known as the blood-tumour barrier (BTB), which is highly heterogeneous and characterized by numerous distinct features, including non-uniform permeability and active efflux of molecules. We discuss the challenges posed by the BBB and BTB for drug delivery, how multiple cell types dictate BBB function and the role of the BTB in disease progression and treatment. Finally, we highlight emerging molecular, cellular and physical strategies to improve drug delivery across the BBB and BTB and discuss their impact on improving conventional as well as emerging treatments, such as immune checkpoint inhibitors and engineered T cells. A deeper understanding of the BBB and BTB through the application of single-cell sequencing and imaging techniques, and the development of biomarkers of BBB integrity along with systems biology approaches, should enable new personalized treatment strategies for primary brain malignancies and brain metastases.

FTY720 (Fingolimod) Ameliorates Brain Injury through Multiple Mechanisms and is a Strong Candidate for Stroke Treatment

FTY720 (Fingolimod) is a known sphingosine-1-phosphate (S1P) receptor agonist that exerts strong anti-inflammatory effects and was approved as the first oral drug for the treatment of multiple sclerosis by the US Food and Drug Administration (FDA) in 2010. FTY720 is mainly associated with unique functional "antagonist" and "agonist" mechanisms. The functional antagonistic mechanism is mediated by the transient down-regulation and degradation of S1P receptors on lymphocytes, which prevents lymphocytes from entering the blood stream from the lymph node. This subsequently results in the development of lymphopenia and reduces lymphocytic inflammation. Functional agonistic mechanisms are executed through S1P receptors expressed on the surface of various cells including neurons, astrocytes, microglia, and blood vessel endothelial cells. These functions might play important roles in regulating anti-apoptotic systems, modulating brain immune and phagocytic activities, preserving the Blood-Brain-Barrier (BBB), and the proliferation of neural precursor cells. Recently, FTY720 have shown receptor-independent effects, including intracellular target bindings and epigenetic modulations. Many researchers have recognized the positive effects of FTY720 and launched basic and clinical experiments to test the use of this agent against stroke. Although the mechanism of FTY720 has not been fully elucidated, its efficacy against cerebral stroke is becoming clear, not only in animal models, but also in ischemic stroke patients through clinical trials. In this article, we review the data obtained from laboratory findings and preliminary clinical trials using FTY720 for stroke treatment.

Apolipoprotein M-bound sphingosine-1-phosphate regulates blood-brain barrier paracellular permeability and transcytosis

The blood-brain barrier (BBB) is formed by the endothelial cells lining cerebral microvessels, but how blood-borne signaling molecules influence permeability is incompletely understood. We here examined how the apolipoprotein M (apoM)-bound sphingosine 1-phosphate (S1P) signaling pathway affects the BBB in different categories of cerebral microvessels using ApoM deficient mice (Apom-/-). We used two-photon microscopy to monitor BBB permeability of sodium fluorescein (376 Da), Alexa Fluor (643 Da), and fluorescent albumin (45 kDA). We show that BBB permeability to small molecules increases in Apom-/- mice. Vesicle-mediated transfer of albumin in arterioles increased 3 to 10-fold in Apom-/- mice, whereas transcytosis in capillaries and venules remained unchanged. The S1P receptor 1 agonist SEW2871 rapidly normalized paracellular BBB permeability in Apom-/- mice, and inhibited transcytosis in penetrating arterioles, but not in pial arterioles. Thus, apoM-bound S1P maintains low paracellular BBB permeability in all cerebral microvessels and low levels of vesicle-mediated transport in penetrating arterioles.

The isolation and molecular characterization of cerebral microvessels

The study of cerebral microvessels is becoming increasingly important in a wide variety of conditions, such as stroke, sepsis, traumatic brain injury and neurodegenerative diseases. However, the molecular mechanisms underlying cerebral microvascular dysfunction in these conditions are largely unknown. The molecular characterization of cerebral microvessels in experimental disease models has been hindered by the lack of a standardized method to reproducibly isolate intact cerebral microvessels with consistent cellular compositions and without the use of enzymatic digestion, which causes undesirable molecular and metabolic changes. Herein, we describe an optimized protocol for microvessel isolation from mouse brain cortex that yields microvessel fragments with consistent populations of discrete blood-brain barrier (BBB) components (endothelial cells, pericytes and astrocyte end feet) while retaining high RNA integrity and protein post-translational modifications (e.g., phosphorylation). We demonstrate that this protocol allows the quantification of changes in gene expression in a disease model (stroke) and the activation of signaling pathways in mice subjected to drug administration in vivo. We also describe the isolation of genomic DNA (gDNA) and bisulfite treatment for the assessment of DNA methylation, as well as the optimization of chromatin extraction and shearing from cortical microvessels. This optimized protocol and the described applications should improve the understanding of the molecular mechanisms governing cerebral microvascular dysfunction, which may help in the development of novel therapies for stroke and other neurologic conditions.

Domain-specific distribution of gap junctions defines cellular coupling to establish a vascular relay in the retina

In the retina, diverse functions of neuronal gap junctions (GJs) have been established. However, the distribution and function of vascular GJs are less clear. Here in the mouse retina whole mounts, we combined structural immunohistochemical analysis and a functional assessment of cellular coupling with a GJ-permeable tracer Neurobiotin to determine distribution patterns of three major vascular connexins. We found that Cx43 was expressed in punctate fashion on astroglia, surrounding all types of blood vessels and in continuous string-like structures along endothelial cell contacts in specialized regions of the vascular tree. Specifically, these Cx43-positive strings originated at the finest capillaries and extended toward the feeding artery. As this structural arrangement promoted strong and exclusive coupling of pericytes and endothelial cells along the corresponding branch, we termed this region a "vascular relay." Cx40 expression was found predominantly along the endothelial cell contacts of the primary arteries and did not overlap with Cx43-positive strings. At their occupied territories, Cx43 and Cx40 clustered with tight junctions and, to a lesser extent, with adhesion contacts, both key elements of the blood-retina barrier. Finally, Cx37 puncta were associated with the entire surface of both mural and endothelial cells across all regions of the vascular tree. This combinatorial analysis of vascular connexins and identification of the vascular relay region will serve as a structural foundation for future studies of neurovascular signaling in health and disease.

Siponimod (BAF-312) Attenuates Perihemorrhagic Edema And Improves Survival in Experimental Intracerebral Hemorrhage

Background and Purpose- Perihemorrhagic edema (PHE) is associated with poor outcome after intracerebral hemorrhage (ICH). Infiltration of immune cells is considered a major contributor of PHE. Recent studies suggest that immunomodulation via S1PR (sphingosine-1-phosphate receptor) modulators improve outcome in ICH. Siponimod, a selective modulator of sphingosine 1-phosphate receptors type 1 and type 5, demonstrated an excellent safety profile in a large study of patients with multiple sclerosis. Here, we investigated the impact of siponimod treatment on perihemorrhagic edema, neurological deficits, and survival in a mouse model of ICH. Methods- ICH was induced by intracranial injection of 0.075 U of bacterial collagenase in 123 mice. Mice were randomly assigned to different treatment groups: vehicle, siponimod given as a single dosage 30 minutes after the operation or given 3× for 3 consecutive days starting 30 minutes after operation. The primary outcome of our study was evolution of PHE measured by magnetic resonance-imaging on T2-maps 72 hours after ICH, secondary outcomes included evolution of PHE 24 hours after ICH, survival and neurological deficits, as well as effects on circulating blood cells and body weight. Results- Siponimod significantly reduced PHE measured by magnetic resonance imaging (P=0.021) as well as wet-dry method (P=0.04) 72 hours after ICH. Evaluation of PHE 24 hours after ICH showed a tendency toward attenuated brain edema in the low-dosage group (P=0.08). Multiple treatments with siponimod significantly improved neurological deficits measured by Garcia Score (P=0.03). Survival at day 10 was improved in mice treated with multiple dosages of siponimod (P=0.037). Mice treated with siponimod showed a reduced weight loss after ICH (P=0.036). Conclusions- Siponimod (BAF-312) attenuated PHE after ICH, increased survival, and reduced ICH-induced sensorimotor deficits in our experimental ICH-model. Findings encourage further investigation of inflammatory modulators as well as the translation of BAF-312 to a human study of ICH patients.

Suppression of transcytosis regulates zebrafish blood-brain barrier function

As an optically transparent model organism with an endothelial blood-brain barrier (BBB), zebrafish offer a powerful tool to study the vertebrate BBB. However, the precise developmental profile of functional zebrafish BBB acquisition and the subcellular and molecular mechanisms governing the zebrafish BBB remain poorly characterized. Here, we capture the dynamics of developmental BBB leakage using live imaging, revealing a combination of steady accumulation in the parenchyma and sporadic bursts of tracer leakage. Electron microscopy studies further reveal high levels of transcytosis in brain endothelium early in development that are suppressed later. The timing of this suppression of transcytosis coincides with the establishment of BBB function. Finally, we demonstrate a key mammalian BBB regulator Mfsd2a, which inhibits transcytosis, plays a conserved role in zebrafish, as mfsd2aa mutants display increased BBB permeability due to increased transcytosis. Our findings indicate a conserved developmental program of barrier acquisition between zebrafish and mice.

Endothelial-Specific Cre Mouse Models

The field of vascular biology has gained enormous insight from the use of Cre and inducible Cre mouse models to temporally and spatially manipulate gene expression within the endothelium. Models are available to constitutively or inducibly modulate gene expression in all or a specified subset of endothelial cells. However, caution should be applied to both the selection of allele and the analysis of resultant phenotype: many similarly named Cre models have divergent activity patterns while ectopic or inconsistent Cre or inducible Cre expression can dramatically affect results. In an effort to disambiguate previous data and to provide a resource to aid appropriate experimental design, here we summarize what is known about Cre recombinase activity in the most widely used endothelial-specific Cre and Cre/ERT2 mouse models.

Sphingosine 1-Phosphate Receptor 1 Signaling Maintains Endothelial Cell Barrier Function and Protects Against Immune Complex-Induced Vascular Injury

OBJECTIVE

Immune complex (IC) deposition activates polymorphonuclear neutrophils (PMNs), increases vascular permeability, and leads to organ damage in systemic lupus erythematosus and rheumatoid arthritis. The bioactive lipid sphingosine 1-phosphate (S1P), acting via S1P receptor 1 (S1P₁ ), is a key regulator of endothelial cell (EC) barrier function. This study was undertaken to investigate whether augmenting EC integrity via S1P₁ signaling attenuates inflammatory injury mediated by ICs.

METHODS

In vitro barrier function was assessed in human umbilical vein endothelial cells (HUVECs) by electrical cell-substrate impedance sensing. Phosphorylation of myosin light chain 2 (p-MLC-2) and VE-cadherin staining in HUVECs were assessed by immunofluorescence. A reverse Arthus reaction (RAR) was induced in the skin and lungs of mice with S1P₁ deleted from ECs (S1P₁ EC-knockout [ECKO] mice) and mice treated with S1P₁ agonists and antagonists.

RESULTS

S1P₁ agonists prevented loss of barrier function in HUVECs treated with IC-activated PMNs. S1P₁ ECKO and wild-type (WT) mice treated with S1P₁ antagonists had amplified RAR, whereas specific S1P₁ agonists attenuated skin and lung RAR in WT mice. ApoM-Fc, a novel S1P chaperone, mitigated EC cell barrier dysfunction induced by activated PMNs in vitro and attenuated lung RAR. Expression levels of p-MLC-2 and disruption of VE-cadherin, each representing manifestations of cell contraction and destabilization of adherens junctions, respectively, that were induced by activated PMNs, were markedly reduced by treatment with S1P₁ agonists and ApoM-Fc.

CONCLUSION

Our findings indicate that S1P₁ signaling in ECs modulates vascular responses to IC deposition. S1P₁ agonists and ApoM-Fc enhance the EC barrier, limit leukocyte escape from capillaries, and provide protection against inflammatory injury. The S1P/S1P₁ axis is a newly identified target to attenuate tissue responses to IC deposition and mitigate end-organ damage.

Lysolipid receptor cross-talk regulates lymphatic endothelial junctions in lymph nodes

Sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) activate G protein-coupled receptors (GPCRs) to regulate biological processes. Using a genome-wide CRISPR/dCas9-based GPCR signaling screen, LPAR1 was identified as an inducer of S1PR1/β-arrestin coupling while suppressing Gαi signaling. S1pr1 and Lpar1-positive lymphatic endothelial cells (LECs) of lymph nodes exhibit constitutive S1PR1/β-arrestin signaling, which was suppressed by LPAR1 antagonism. Pharmacological inhibition or genetic loss of function of Lpar1 reduced the frequency of punctate junctions at sinus-lining LECs. Ligand activation of transfected LPAR1 in endothelial cells remodeled junctions from continuous to punctate structures and increased transendothelial permeability. In addition, LPAR1 antagonism in mice increased lymph node retention of adoptively transferred lymphocytes. These data suggest that cross-talk between LPAR1 and S1PR1 promotes the porous junctional architecture of sinus-lining LECs, which enables efficient lymphocyte trafficking. Heterotypic inter-GPCR coupling may regulate complex cellular phenotypes in physiological milieu containing many GPCR ligands.

Editing the Central Nervous System Through CRISPR/Cas9 Systems

The translational gap to treatments based on gene therapy has been reduced in recent years because of improvements in gene editing tools, such as the CRISPR/Cas9 system and its variations. This has allowed the development of more precise therapies for neurodegenerative diseases, where access is privileged. As a result, engineering of complexes that can access the central nervous system (CNS) with the least potential inconvenience is fundamental. In this review article, we describe current alternatives to generate systems based on CRISPR/Cas9 that can cross the blood-brain barrier (BBB) and may be used further clinically to improve treatment for neurodegeneration in Parkinson's and Alzheimer's disease (AD).

Quantification of 3D Brain Microangioarchitectures in an Animal Model of Krabbe Disease

We performed a three-dimensional (3D) analysis of the microvascular network of the cerebral cortex of twitcher mice (an authentic model of Krabbe disease) using a restricted set of indexes that are able to describe the arrangement of the microvascular tree in CD31-stained sections. We obtained a near-linear graphical "fingerprint" of the microangioarchitecture of wild-type and twitcher animals that describes the amounts, spatial dispersion, and spatial relationships of adjacent classes of caliber-filtered microvessels. We observed significant alterations of the microangioarchitecture of the cerebral cortex of twitcher mice, whereas no alterations occur in renal microvessels, which is keeping with the observation that kidney is an organ that is not affected by the disease. This approach may represent an important starting point for the study of the microvascular changes that occur in the central nervous system (CNS) under different physiopathological conditions.

Sphingosine 1-phosphate receptor 1 regulates cell-surface localization of membrane proteins in endothelial cells

The endothelial cell (EC) barrier disruption has been implicated in vascular leakage and pulmonary edema. Many reports have shown that the EC barrier dysfunction is regulated by the sphingosine-1-phophate (S1P)/S1P receptor-1 (S1PR1) axis. Identifying downstream effectors for the S1P/S1PR1 axis in pulmonary vasculature has been limited by mixed populations in vitro cultures that do not retain physiological EC phenotype and complex of tedious proteomics. In this study, we used a combination of in vivo biotinylation and liquid chromatograph tandem mass spectrometry on three mouse models of S1pr1 expression, namely normal, knockout (KO) and high, to identify EC membrane proteins whose cell-surface expression is S1pr1-dependent. EC-specific KO of S1pr1 caused severe pulmonary vascular disruption and reduction of many membrane proteins on ECs. Using the MaxQuant software we were able to identify novel membrane targets of S1pr1, for instance, Cd105 and Plvap, by comparison with their membrane expressions among the three EC model systems. Moreover, regulation of Cd105 and Plvap by S1pr1 were validated with Western blot and immunostaining in vivo and in vitro. Our data suggest that S1pr1 dictates cell-surface localization of several apical membrane proteins in ECs. Our results are insightful for development of novel therapeutics to specifically target EC barrier function.

Sphingosine 1-phosphate induces epicardial progenitor cell differentiation into smooth muscle-like cells

Epicardial progenitor cells (EpiCs) which are derived from the proepicardium have the potential to differentiate into coronary vascular smooth muscle cells during development. Whether sphingosine 1-phosphate (S1P), a highly hydrophobic zwitterionic lysophospholipid in signal transduction, induces the differentiation of EpiCs is unknown. In the present study, we demonstrated that S1P significantly induced the expression of smooth muscle cell specific markers α-smooth muscle actin and myosin heavy chain 11 in the EpiCs. And the smooth muscle cells differentiated from the EpiCs stimulated by S1P were further evaluated by gel contraction assay. To further confirm the major subtype of sphingosine 1-phosphate receptors (S1PRs) involved in the differentiation of EpiCs, we used the agonists and antagonists of different S1PRs. The results showed that the S1P1/S1P3 antagonist VPC23019 and the S1P2 antagonist JTE013 significantly attenuated EpiCs differentiation, while the S1P1 agonist SEW2871 and antagonist W146 did not affect EpiCs differentiation. These results collectively suggested that S1P, principally through its receptor S1P3, increases EpiCs differentiation into VSMCs and thus indicated the importance of S1P signaling in the embryonic coronary vasculature, while S1P2 plays a secondary role.

Development of the brain vasculature and the blood-brain barrier in zebrafish

To ensure tissue homeostasis the brain needs to be protected from blood-derived fluctuations or pathogens that could affect its function. Therefore, the brain capillaries develop tissue-specific properties to form a selective blood-brain barrier (BBB), allowing the passage of essential molecules to the brain and blocking the penetration of potentially harmful compounds or cells. Previous studies reported the presence of this barrier in zebrafish. The intrinsic features of the zebrafish embryos and larvae in combination with optical techniques, make them suitable for the study of barrier establishment and maturation. In this review, we discuss the most recent contributions to the development and formation of a functional zebrafish BBB. Moreover, we compare the molecular and cellular characteristic of the zebrafish and the mammalian BBB.

Mechanism of Siponimod: Anti-Inflammatory and Neuroprotective Mode of Action

Multiple sclerosis (MS) is a neuroinflammatory disorder of the central nervous system (CNS), and represents one of the main causes of disability in young adults. On the histopathological level, the disease is characterized by inflammatory demyelination and diffuse neurodegeneration. Although on the surface the development of new inflammatory CNS lesions in MS may appear consistent with a primary recruitment of peripheral immune cells, questions have been raised as to whether lymphocyte and/or monocyte invasion into the brain are really at the root of inflammatory lesion development. In this review article, we discuss a less appreciated inflammation-neurodegeneration interplay, that is: Neurodegeneration can trigger the formation of new, focal inflammatory lesions. We summarize old and recent findings suggesting that new inflammatory lesions develop at sites of focal or diffuse degenerative processes within the CNS. Such a concept is discussed in the context of the EXPAND trial, showing that siponimod exerts anti-inflammatory and neuroprotective activities in secondary progressive MS patients. The verification or rejection of such a concept is vital for the development of new therapeutic strategies for progressive MS.

Quantitative iTRAQ-based proteomic analysis of piperine protected cerebral ischemia/reperfusion injury in rat brain

Piperine is the key bioactive factor in black pepper, and has been reported to alleviate cerebral ischemic injury. However, the mechanisms underlying its neuroprotective effects following cerebral ischemia remain unclear. In this study, rats were administered vehicle (dimethyl sulfoxide) or piperine, 20 mg/kg, daily for 14 days before focal cerebral artery occlusion. After occlusion for 2 h followed by reperfusion for 24 h. Histological examinations were used to assess whether piperine has a neuroprotective effect in the rat model of cerebral ischemia/reperfusion injury. The levels of proteins in the ischemic penumbra were evaluated by isobaric tags for relative and absolute quantitation-based proteomics. A total of 3687 proteins were identified, including 23 proteins that were highly significantly differentially expressed between the control and piperine groups. The proteomic findings were verified by immunofluorescence and western blot analysis. Interestingly, piperine administration downregulated a number of critical factors in the complement and coagulation cascades, including complement component 3, fibrinogen gamma chain, alpha-2-macroglobulin, and serpin family A member 1. Collectively, our findings suggest that the neuroprotective effects of piperine following cerebral ischemia/reperfusion injury are related to the regulation of the complement and coagulation cascades.

Effective and Targeted Human Orthotopic Glioblastoma Xenograft Therapy via a Multifunctional Biomimetic Nanomedicine

Glioblastoma multiforme (GBM) is a fatal central nervous system tumor without effective treatment. Chemotherapeutic agents are mainstays in the treatment of glioblastoma. However, the effectiveness of these is seriously hindered by poor blood-brain-barrier (BBB) penetrance and tumor targeting, together with short biological half-life. Improved chemotherapy is thus urgently needed for GBM. Multifunctional nanoparticle delivery systems offer much promise in overcoming current limitations. Accordingly, a multifunctional biomimetic nanomedicine is developed by functionalizing the surface of red blood cell membranes (RBCms) with angiopep-2 and loading pH-sensitive nanoparticles (polymer, doxorubicin (Dox), and lexiscan (Lex)) using the functionalized cell membrane to generate the novel nanomedicine, Ang-RBCm@NM-(Dox/Lex). The studies toward orthotopic U87MG human glioblastoma tumor-bearing nude mice show that the Ang-RBCm@NM-(Dox/Lex) nanomedicine has much improved blood circulation time, superb BBB penetration, superior tumor accumulation and retention. Moreover, effective suppression of tumor growth and significantly improved medium survival time are also observed after Ang-RBCm@NM-(Dox/Lex) treatment. The results show that this biomimetic nanoplatform can serve as a flexible and powerful system for GBM treatment which can be readily adapted for the treatment of other central nervous system (CNS) disorders.

Wnt/β-catenin signaling regulates VE-cadherin-mediated anastomosis of brain capillaries by counteracting S1pr1 signaling

Canonical Wnt signaling is crucial for vascularization of the central nervous system and blood-brain barrier (BBB) formation. BBB formation and modulation are not only important for development, but also relevant for vascular and neurodegenerative diseases. However, there is little understanding of how Wnt signaling contributes to brain angiogenesis and BBB formation. Here we show, using high resolution in vivo imaging and temporal and spatial manipulation of Wnt signaling, different requirements for Wnt signaling during brain angiogenesis and BBB formation. In the absence of Wnt signaling, premature Sphingosine-1-phosphate receptor (S1pr) signaling reduces VE-cadherin and Esama at cell-cell junctions. We suggest that Wnt signaling suppresses S1pr signaling during angiogenesis to enable the dynamic junction formation during anastomosis, whereas later S1pr signaling regulates BBB maturation and VE-cadherin stabilization. Our data provides a link between brain angiogenesis and BBB formation and identifies Wnt signaling as coordinator of the timing and as regulator of anastomosis.

Fingolimod reduces circulating tight-junction protein levels and in vitro peripheral blood mononuclear cells migration in multiple sclerosis patients

There are no data on the effects of fingolimod, an immunomodulatory drug used in treatment of multiple sclerosis (MS), on circulating tight-junction (TJ) protein levels as well as on peripheral blood mononuclear cells (PBMC) migration. Serum TJ protein [occludin (OCLN), claudin-5 (CLN-5) and zonula occludens-1 (ZO-1)] levels, sphingosine-1 phosphate 1 (S1P₁) receptor expression on circulating leukocyte populations as well as in vitro PBMC migration were longitudinally assessed in 20 MS patients under 12-months fingolimod treatment and correlated with clinical and magnetic resonance imaging (MRI) parameters. After 12 months of treatment, a significant reduction of mean relapse rate as well as number of active lesions at MRI was found. TJ protein levels significantly decreased and were associated with reduction of S1P₁ expression as well as of PBMC in vitro migratory activity. A significant correlation of CLN-5/OCLN ratio with new T₂ MRI lesions and a significant inverse correlation of CLN-5/ZO-1 ratio with disability scores were found. These findings support possible in vivo effects of fingolimod on the blood-brain barrier (BBB) functional activity as well as on peripheral cell trafficking that could result in avoiding passage of circulating autoreactive cells into brain parenchyma. Circulating TJ protein levels and respective ratios could be further studied as a novel candidate biomarker of BBB functional status to be monitored in course of fingolimod as well as of other immunomodulatory treatments in MS.